Retroreflective articles have the ability to redirect obliquely incident light back towards the light source. This unique ability has led to the wide-spread use of retroreflective articles on various substrates. For example, retroreflective articles can be used on flat, inflexible substrates, such as road signs and barricades; on irregular surfaces, such as corrugated metal truck trailers, license plates, and traffic barriers; and on flexible substrates, such as road worker safety vests, a jogger's shoes, roll up signs, and canvas-sided trucks. Retroreflective articles are also employed for various other safety as well as decorative purposes. Retroreflective articles are particularly useful in low-light conditions to improve safety by retroreflecting light incident thereon to the source of the incident light.
Retroreflective articles are typically used on clothing to increase the visibility of the individual by retroreflecting the incident light. The retroreflective articles that are utilized on clothing include strips of tape that are adhered to clothing with heat sensitive adhesive, patches permanently affixed or sewn to the clothing, and articles of clothing that include a retroreflective article within the clothing. Retroreflective clothing is especially useful to construction workers and exercisers who utilize roadways because these individuals are in close proximity to moving vehicles on a regular basis and the retroreflective articles make the individuals more visible to drivers under low light conditions.
Retroreflective articles typically utilize a highly plasticized polyvinyl chloride (PVC) film as an overlying sheet for passing light to a retroreflective structure that includes, for example, cube-corner reflecting elements. However, plasticizers have a tendency to migrate from PVC film. Accordingly, over time plasticized PVC films lose temperature stability and flexibility (especially in cold weather). Also, plasticizers are used to enhance flexibility of polyvinyl chloride (PVC) films. However, plasticizers make PVC films exhibit relatively low softening temperatures (e.g., 180° F.). Such low softening temperatures tend to place constraints on commercial manufacture of retroreflective articles including plasticized PVC film since the latter do not possess sufficient rigidity for efficient web transportation through the manufacturing process. For example, cube-corner reflecting elements when cast or joined to the plasticized PVC film are typically cured at temperatures higher than the softening temperatures of the PVC film. To compensate for this softening, additional polyester layers, such as a top sheet and a releasable backing sheet that do not soften at cube-corner curing temperatures are typically joined to the plasticized PVC films. While enabling efficient web transportation, these additional layers add to overall manufacturing costs and are ultimately discarded. Furthermore, annealing plasticized PVC films following curing of cast cube-corners is required to overcome detrimental affects induced by softening. Annealing, however, adds to overall manufacturing energy costs. Some plasticizers, such as di octyl phthalate (DOP) are reported to have health risks to young children. Other long-term durability issues are also created when using plasticized PVC film.